Conditionals in XAML

Published on 03 december 2017

Ever wanted to display things conditionally in XAML based on a pre-processor directive like DEBUG?

Start by adding the following to your AssemblyInfo.cs

#if DEBUG
[assembly: XmlnsDefinition("http://github.com/me/myproject/debug", "MyProjectNamespace")]
#endif

Now, in your XAML file, you should be able to add a new namespace pointing to this definition. We also need to import the XAML compatibility namespace. To suppress the errors given by the XAML processor, use the mc:Ignorable attribute.

You should now be able to use AlternateContent, Choice and (optionally) Fallback elements in your XAML code to show different elements depending on your build configuration.

<Window x:Class="MyProjectNamespace.MyView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:debug="http://github.com/me/myproject/debug"
    mc:Ignorable="mc">

    <mc:AlternateContent>
        <mc:Choice Requires="debug">
            <TextBlock Text="Debugging!" />
        </mc:Choice>
        <mc:Fallback>
            <TextBlock Text="Not debugging!" />
        </mc:Fallback>
    </mc:AlternateContent>

</Window>

Be aware that content within AlternateContent will not show in the designer. If this is something you need, I recommend that you use a different technique.

Update (2017-12-05)

The AlternateContent element doesn't seem to be supported in UWP applications.